Zambian President Kenneth Kaunda announced yesterday that his country is partially liftin gits economic blockade imposed on neighboring Rhodesia five years ago in a bid to bring down the white-dominated biracial government there.

At a news conference in Lusaka, the Zambian leader said he was opening the southern rail route linking South Africa and Zambia via Rhodesia to facilitate the export of vital Zambian copper and the import of a wide variety of basic goods into his economically hard-pressed landlocked nation.

"However, this does not mean the reopening of the entire border nor trade with Rhodesia," he quickly added. "There will be no effect on the liberation struggle" of Rhodesia's black nationalists.

At the same, President Kaunda sharply criticized the Carter administration for allowing Rhodesian Prime Minister Ian Smith to enter the United States this weekend. Calling Smith "a white racist, an arch racist, a killer." Kaunda angrily warned that his trip would trigger "the final stage of confrontation" over Rhodesia.

"Let them not forget that they are starting a new Vietnam in southern Africa" he added.

The exact impact of the Zambian decision on the war in Rhodesia was not immediately clear. Kaunda said Zambia still had no intention of trading path its neighbor or of opening up the entire border to normal traffic.

This aside from the money Rhodesia will earn from transit fees on Zambian goods moving on its railroad, the opening of the southern rail route would appear to bring little relief to the equally hard pressed Rhodesian economy.

Moreover, it is far from clear that Zambia will be able to pay immediately even these transit fees given its state of near bankruptcy unless South Africa provides it with a loan.

But the decision may have an important psychological impact on the isolated and economically strained biracial transitional government now ruling Rhodesia, giving rise to hopes that Zambia may next normalize its trade relations with it, if not extend diplomatic recognition.

The Zambian decision came as a major crisis was developing over the export of its copper, which provides more than 90 percent of its foreign exchange earnings and the import of fertilizer badly needed for the coming year's corn crop.

Zambian and foreign economists are blocked in ports in Mozambique copper are now tied up along the Chinese-built Zambian-Tanzanian Railroad or in the congrested Tanzanian port of Dar es Salaam. At the same time, about 90,000 tons of fertilizers are blocked in ports in Mozambique and South Africa or along a complicated rail and road route through Botswana.

Zambia's inability to get the fertilizer into the country before the rains start in about a month was believed to be the final straw in President Kaundas decision to relent on the economic blockade of Rhodesia and to begin using again the Rhodesian railroad systems. Without the fertilizer, Zambia stood to lose as much as half of its normal harvest of corn, the key staple food of the country's 5 million inhabitants.

However, the presidential and general elections scheduled for Dec. 12 were also seen here as an important political factor in the Zambian leader's calculations.

Discontent has been steadily building up during the past year over shortages of such basic commodities as sugar, cooking oil, milk, butter, rice and flour.

Despite a nearly $400 million loan from the International Monetary Fund early this year, the economic situation in Zambia has failed to improve noticeably. This has been partly because of the multiple bottlenecks along the various rail and road routes leading into the country.

Even the payment of the first slice of the IMF loan, amounting to more than $100 million, seems to have made little impact on these chronic shortages. The money is mostly being used to pay off some of the $500 million in Zambian arrears on imports in order to re-establish lines of credit allowing the government to resume the purchase abroad of essential goods.

Zambian officials were quoted by Reuter News Agency in Lusaka as saying the opening of the southern route would bring a wide variety of basic commodities back into the country. But they were officially denying that the decision was made because of the forthcoming elections.

President Kaunda said he had consulted the other Afriacan "front-line" states in the Rhodesian conflict - Tanzania, Mozambique, Botswana and Angola - and had gotten a "sympathetic response" from their presidents regarding his decision.

The Zambian leader was here in Maputo for talks with President Samora Machel earlier this week and sent his highest ranking aides to the other three front-line capitals to explain his decision.

However, sources here said Mozambique was not at all pleased with the Zambian leader's action while a spokesman for the Mozambique-based wing of the Patriotic Front, the Rhodesian nationalist guerrilla alliance, was openly critical of it.

Ironically, for the past five years Zambia has avoided shipping its copper and receiving goods through Rhodesia by using the railroad system of white-dominated South Africa.

Before yesterday's announcement, Zambia received fertilizer unloaded in the Mozambique ports of Maputo and Beira and the port of Durban in South Africa. The fertilizer was then shipped by train through South Africa to Francistown, Botswana, and then by truck to Kazangula and Livingstone, both in southern Zambia.